Current control device

ABSTRACT

A device for controlling an electrical current through a load by means of a bilateral controlled rectifying element. Said element is fired periodically through a bilateral rectifier which in its turn receives a firing signal through a series capacitor included in the output circuit of a control amplifier, which at its input receives stimuli for firing said controlled rectifying element. Said series capacitor is effective to improve the symmetry of the waveform of the current through the load, while also the current control range is increased thereby.

United States Patent Laupman 1 51 Jan. 25, 1972 [54] CURRENT CONTROLDEVICE [72] Inventor: Robert Ronald Laupman, Wijchen,

Netherlands [73] Assignee: N. V. Auco, Wijchen, Netherlands {22] Filed:Oct. 6, 1969 [21] Appl.No.: 863,891

[30] Foreign Application Priority Data Oct. 9, 1968 Netherlands..68/14,447

[52] [1.8. CI. ..307/252 B, 307/252 N, 307/295,

51 Int/Cl. ..H03k17/00 58 Field of Search ..307/25221, 252.70, 305, 29s

[56] References Cited UNlTED STATES PATENTS 2,871,305 1/1959 Hurtig..307/293 Gutzwiller ..307/253 3,353,078 11/1967 Maynard... ..307/2523,443,124 5/1969 Pinckaers ..307/305 3,513,332 5/1970 Snyder ..307/252Primary Examiner-Donald D. Forrer Assistant ExaminerDavid M. CarterAttorny-Diller, Brown, Ramik & Holt 57 ABSTRACT A device for controllingan electrical current through a load by means of a bilateral controlledrectifying element. Said element is fired periodically through abilateral rectifier which in its turn receives a firing signal through aseries capacitor included in the output circuit of a control amplifier,which at its input receives stimuli for firing said controlledrectifying element. Said series capacitor is effective to improve thesymmetry of the waveform of the current through the load, while also thecurrent control range is increased thereby.

16 Claims, 7 Drawing Figures PAIENIEOmzsmz 3.638.043

saw-10F 3 INVENTOR.

' E k -w gimw hu PATENTED JANZS I972 ma-W5 CURRENT CONTROL DEVICE It isknown to control the AC voltage generated across a load, using a triodesemiconductor ACswitching means, such as a triac, which is connected tothe AC supply mains in series with the load. The gate electrode of thetriode semiconductor AC switching means in that case connected through adiode semiconductor AC switching means, such as adiac, with the nodalpoint of a series circuit formed by a variable resistor and a capacitor,which series circuit is connected in parallel with the triodesemiconductor AC switching means, or triac.

There'are a good many drawbacks inherent in such-a relatively simplecircuit, which is shown diagrammatically in FIG.

voltage is produced, so that such a resistor must be of excellentquality. To obviate the first-mentioned drawback, circuits of theabove-known type have been designed in accordance with likewise knownproposals, as shown in FIG. 1 by the dashed lines.

In addition tothe above drawbacks this circuit has the serious drawbackthat is is actually unsuitable for controlling purposes, for instanceusing a light-sensitive resistor (LDR-resistor), a temperature-sensitiveresistor (NTC-resistor), or like elements, on account of the extremelylow sensitivity.

The object of the invention is to provide the simplest possible solutionfor all the above drawbacks. Thus it is even possible'to simplyintroduce a delay by means of which it is possible to entirely suppresscurrent pulses owing to for instance the occurrence of relatively rapidvoltage variations in an inductive load.

The invention is particularly applicable to cases in which the load is aDC motor connected ina diode bridge circuit. In that case, if the motoris inoperative and the supply mains is suddenly switched on, while thecontrol voltage divider is adjusted for the maximum speed, relativelystrong currents may flow which only reach their normal value when themotor and the transmission means connected therewith have reached theirfinal speed.

Such a situation arises when the dividing ratio of the control voltagedivider is varied at relatively high speed.

A properly dimensioned voltage generated with delay across the load willin this case save the motor (commutator), drive mechanism (gearbox) andcontrol means (peak currents).

FIG. I is prior art. FIGS. 2-7 are embodiments of the invention.

An embodiment of a circuit according to the invention is shown in FIG.2. A series circuit comprising a load B and a triode semiconductor ACcurrent switching means T, is connected across the supply mains. Aseries circuit formed by a resistor R, and a capacitor C, is connectedin parallel with this switching means T,,. The nodal point of thisresistor R, and capacitor C, is connected through a diode AC switchingmeans D, with the gate electrode of the switching means T,,. The ACvoltage input of a bridge circuit comprising diodes D,D, is connectedthrough capacitor C, across capacitor C,.

A control amplifier RV is connected with the DC voltage terminals ofthis bridge circuit. The control input of this control amplifier isconnected with the tap of a voltage divider formed by two impedances Z,and Z;,, the ends of which voltage divider are also connected with theDC voltage terminals of the bridge circuit.

When properly dimensioning the component parts and by varying thevoltage divider formed by the impedances Z, and Z, it is possible toform a control range wherein the voltage generated across the load canbe controlled from zero to a maximum value. The capacitor C, isessential iii the sense that owing to the presence of this capacitorrelatively small cutoff angles .of the voltage waveform can be realizedtoo. If there sli'oiild be a difference between the cutoff angles ofsuccessive sine halves, a magnitude characteristic of such a differencecan be found in the form of a residual voltage on capacitor C,, whosecapacitance is higher thanthat of capacitor C,. Such a residual voltagethen forms a'control voltage which isactive in the next sine half tocompensate for thisdifference.

The embodiment of FIG. 2 is shown in greater detail in FIG. 3, inwhichthe controlamplifier RV is designe'dsimplest in the form of anamplifier provided with a transistor 'I.,. In the circuit shown in FIG.3, a diode or a Zener diode D, has been connectedin series with theemitter of thetransistor T, of the control amplifier RV, in order toobtain an improvement of the control effect. If for example the resistorR, of this circuit is replaced by anNTC-resistor, or if the resistor R,isfully or partly replaced by a light-sensitive resistor, it appearsthat taking into account the simplicity of the device, unexpectedly highsensitivities are obtained. By connecting a resistor R, between the baseof the transistor T, and the node of resistor R, it is possible toinfluence the control characteristic, which is often desirable innonlinear transducers such as NTC-resistors.

By connecting a capacitor C, between the base andthe collector oftransistor T,, a delay is simply introduced in the sense that in case ofa rapid variation of the resistor R, the control effect of transistor T,is delayed by said capacitor C,. It appears to be possible to realize adelay in the order of magnitude of some seconds, with an order ofmagnitude of some microfarads for the capacitance of this capacitor C Inorder that this capacitor C, does not discharge during and adjacent thezero places of the sine wave, a capacitor C, may be connected across theDC voltage terminals of the bridge circuit with diodes D',-D,,, whichcapacitor keeps the voltage constant during these periods. I

As a matter of course it is possible to utilize in the circuit accordingto the invention more complicated control amplifiers having one or morecontrol or logic inputs of higher sensitivity. I

FIG. 4 shows a variant of the circuits shown in FIGS. 2 and 3, moreparticularly a variant of the section of the circuit to the right ofcapacitor C, In the embodiment shown in FIG. 4 the control amplifierwith transistor T, is formed with one input circuit having a diode D anda second input circuit having a diode D The input circuit having thediode D is coupled with a temperature-sensitive circuit with atransistor T, and an NTC-resistor R,,. The input circuit having thediode I), is coupled with a voltage divider formed by the resistors R R,and R,, with which a minimum value can be adjusted at choice. Thecontrolling effect of transistor T, is always determined by either ofthe two voltages applied on the cathode side of the diodes D, and D, inquestion, that is the voltage which is the lower under thecircumstances.

In the embodiment as shown in FIG. 2 the impedances Z, and Z, of thevoltage divider may take different forms. Not only are these impedancesZ, and Z, formed as resistors, but the impedance Z, may for example be acapacitor and resistor connected in parallel. FIG. 5 shows analternative embodiment in which the impedance Z, comprises a seriescircuit formed by a resistor R,, and a capacitor C,,, while impedance Z,is famed by a resistor R and a capacitor C, connected in parallel. Withthe embodiment shown in FIG. 5 it is possible to dimension the componentparts in such a manner that the load is intermittently connected to thevoltage, to allow for a cycle duration of some seconds.

FIG. 6 shows an embodiment in which the present invention has beenapplied in the event that the load is adapted for connection to athree-phase supply mains R, S, T. The characters designating partscorresponding with the embodiments shown in FIGS. 2 and 3 are for eachphase provided with apostrophes in the embodiment shown in FIG. 6, whilethe bridge circuit with the diodes D ,,-D,,, is adapted to thethree-phase system. The embodiment of FIG. 6 has the advantage thatthere may be a simple coupling between the phases, so that the devicecan be realized in a simple manner and with relatively few parts.

FIG. 7 shows a variant of the circuit shown in FIG. 6. This variant isparticularly suitable for those cases where of the three-phase load onlythe star point is accessible for external connection. In this case,however, it is necessary to provide for each phase a galvanic separationbetween the diac and triac in question, so that the firing energy isthen transmitted through an associated coupling transformer KT'KT' Iclaim:

A current control device comprising an alternating current thyristorhaving a control electrode and two current-carrying electrodes; meansfor connecting said two current-carrying electrodes in series with aload to an alternating current supply; a RC circuit connected inparallel-with said two current carrying electrodes; an alternatingcurrent diode having first and second electrodes coupled between saidcontrol electrode and a point on said RC circuit; a capacitance means; arectifying circuit having two input terminals and two output terminals,said capacitance means being coupled between one of said input terminalsof said rectifying circuit and said point on said RC circuit, and theother of said input terminals of said rectifying circuit being coupledto one of the current-carrying electrodes of said alternating currentthyristor; a control amplifier having a control electrode and two mainelectrodes, said two main electrodes being coupled across the two outputterminals of said rectifying circuit; and a condition-sensing voltagedivider means for developing a control signal at a tap thereon, said tapbeing coupled to the control electrode of said control amplifier.

2. A current control device according to claim 1 wherein saidcondition-sensing voltage divider means is coupled across said outputterminals of said rectifying circuit.

3. A current control device according to claim 1 wherein said controlamplifier comprises a transistor amplifier having a collector electrode,an emitter electrode and a base electrode, and a resistance means iscoupled between the base electrode of said transistor and said tap onthe condition-sensing voltage divider means.

4. A current control device according to claim 3 including a diode meanscoupled between said emitter electrode and one of the output terminalsof said rectifying circuit.

5. A current control device according to claim 3 including a capacitivemeans coupled between said collector electrode and said base electrode.

6. A current control device according to claim 4 including a capacitivemeans coupled between said collector electrode and said base electrode.

7. A current control device according to claim 3 wherein a capacitivemeans is coupled between said collector electrode and said emitterelectrode.

8. A current control device according to claim 4 wherein a capacitivemeans is coupled between said collector electrode and said emitterelectrode.

9. A current control device according to claim 5 wherein a capacitivemeans is coupled between said collector electrode and said emitterelectrode.

10. A current control device according to claim 6 wherein a capacitivemeans is coupled between said collector electrode and said emitterelectrode.

11. A current control device according to claim 1 wherein said controlelectrode of said control amplifier is coupled to a terminal of each ofa plurality of diodes, the other terminal of each of said plurality ofdiodes being coupled to points on said condition-sensing voltage dividermeans.

12. A current device according to claim 1 comprising a plurality ofalternating current thyristors each having a control electrode and twocurrent carrying electrodes; a plurality of means for connecting eachsaid two current carrying electrodes in series with respective loads torespective difi'erent phases of an alternating current supply; aplurality of RC circuits connected respectively in parallel with eachrespective said two currentcarrying electrodes; a plurality ofalternating current diodes each having first and second electrodescoupled respectively between one of said control electrodes and a pointon a respectwe one of said plurality of RC circuits; a plurality ofcapacitive means; a plurality of rectifying circuits each having twoinput terminals and two output terminals,

' each of said plurality of capacitive means being coupled respectivelybetween one of said input terminals of one of said plurality ofrectifying circuits and the said point on respective ones of saidplurality of RC circuits; and means for coupling the two outputterminals of each of said plurality of rectifying circuits across thetwo main electrodes of said control amplifier.

13. A current control device according to claim 12 wherein each of therespective loads has a first terminal connected to a respective one ofsaid two current-carrying electrodes of each of said plurality ofalternating current thyristors, respectively; each of the respectiveloads has a second terminal connected in common with the secondterminals of all other loads to define a star point; and each of saidplurality of alternating current diodes is connected with individualmagnetic coupling means coupled respectively between one of saidcurrent-carrying electrodes and the control electrode of each ;of saidplurality of alternating current thyristors.

14. A current control device according to claim 12 wherein saidcondition-sensing voltage divider means is coupled across said twooutput terminals of each of said plurality of rectifying circuits.

15. A current control device according to claim l3 wherein saidcondition-sensing voltage divider means is coupled across said twooutput terminals of each of said plurality of rectifying circuits.

16. A current control device according to claim 4 wherein said diodemeans is a Zener diode.

1. A current control device comprising an alternating current thyristorhaving a control electrode and two current-carrying electrodes; meansfor connecting said two current-carrying electrodes in series with aload to an alternating current supply; a RC circuit connected inparallel with said two current carrying electrodes; an alternatingcurrent diode having first and second electrodes coupled between saidcontrol electrode and a point on said RC circuit; a capacitance means; arectifying circuit having two input terminals and two output terminals,said capacitance means being coupled between one of said input terminalsof said rectifying circuit and said point on said RC circuit, and theother of said input terminals of said rectifying circuit being coupledto one of the current-carrying electrodes of said alternating currentthyristor; a control amplifier having a control electrode and two mainelectrodes, said two main electrodes being coupled across the two outputterminals of said rectifying circuit; and a condition-sensing voltagedivider means for developing a control signal at a tap thereon, said tapbeing coupled to the control electrode of said control amplifier.
 2. Acurrent control device according to claim 1 wherein saidcondition-sensing voltage divider means is coupled across said outputterminals of said rectifying circuit.
 3. A Current control deviceaccording to claim 1 wherein said control amplifier comprises atransistor amplifier having a collector electrode, an emitter electrodeand a base electrode, and a resistance means is coupled between the baseelectrode of said transistor and said tap on the condition-sensingvoltage divider means.
 4. A current control device according to claim 3including a diode means coupled between said emitter electrode and oneof the output terminals of said rectifying circuit.
 5. A current controldevice according to claim 3 including a capacitive means coupled betweensaid collector electrode and said base electrode.
 6. A current controldevice according to claim 4 including a capacitive means coupled betweensaid collector electrode and said base electrode.
 7. A current controldevice according to claim 3 wherein a capacitive means is coupledbetween said collector electrode and said emitter electrode.
 8. Acurrent control device according to claim 4 wherein a capacitive meansis coupled between said collector electrode and said emitter electrode.9. A current control device according to claim 5 wherein a capacitivemeans is coupled between said collector electrode and said emitterelectrode.
 10. A current control device according to claim 6 wherein acapacitive means is coupled between said collector electrode and saidemitter electrode.
 11. A current control device according to claim 1wherein said control electrode of said control amplifier is coupled to aterminal of each of a plurality of diodes, the other terminal of each ofsaid plurality of diodes being coupled to points on saidcondition-sensing voltage divider means.
 12. A current control deviceaccording to claim 1 comprising a plurality of alternating currentthyristors each having a control electrode and two current carryingelectrodes; a plurality of means for connecting each said two currentcarrying electrodes in series with respective loads to respectivedifferent phases of an alternating current supply; a plurality of RCcircuits connected respectively in parallel with each respective saidtwo current-carrying electrodes; a plurality of alternating currentdiodes each having first and second electrodes coupled respectivelybetween one of said control electrodes and a point on a respective oneof said plurality of RC circuits; a plurality of capacitive means; aplurality of rectifying circuits each having two input terminals and twooutput terminals, each of said plurality of capacitive means beingcoupled respectively between one of said input terminals of one of saidplurality of rectifying circuits and the said point on respective onesof said plurality of RC circuits; and means for coupling the two outputterminals of each of said plurality of rectifying circuits across thetwo main electrodes of said control amplifier.
 13. A current controldevice according to claim 12 wherein each of the respective loads has afirst terminal connected to a respective one of said twocurrent-carrying electrodes of each of said plurality of alternatingcurrent thyristors, respectively; each of the respective loads has asecond terminal connected in common with the second terminals of allother loads to define a star point; and each of said plurality ofalternating current diodes is connected with individual magneticcoupling means coupled respectively between one of said current-carryingelectrodes and the control electrode of each of said plurality ofalternating current thyristors.
 14. A current control device accordingto claim 12 wherein said condition-sensing voltage divider means iscoupled across said two output terminals of each of said plurality ofrectifying circuits.
 15. A current control device according to claim 13wherein said condition-sensing voltage divider means is coupled acrosssaid two output terminals of each of said plurality of rectifyingcircuits.
 16. A current control device according to claim 4 wherein saiddiode means is a Zener diodE.